Treatment of materials in rotating furnaces or drums by hot gas



' Nov. 12, 1935. v v J. M. PEHRSON El AL 2,020,950

TREATMENT OF MATERIALS I N ROTATING FURNACES OR DRUMS BY HOT GAS Filed Jan. 27 1954 WITNESSES: mvc/v-roRs:

Patented Nov. 12, 1935 UNITED STATES REATMENT OF MATERIALS IN ROTATING FURNACES on DRUMS BY no'r GAS Johan Marten Pehrson and Ragnar Viktor Pehrson, Stockholm, Sweden Application January 2'7, 1934, Serial No. 7081710 In Finland October 24, 1933 4 Claims.

The present invention relates to treatment of a charge of material in a rotating furnace or drum by hot gas, said drum having a perforated shell or a shell provided with openings or slots,

' 5 the gas being introduced into and passed through the charge, along the whole or approximately the whole length of the shell through a suitable number of the holes, openings or slots in said shell which are covered by the charge from a gas supply box or boxes, chambers or the like not taking part in the rotation of the drum and contiguous to or abutting against the shell by the intermedium of suitable packing means, said box or boxes or the like communicating with a fan, pump or the like for forwarding the gas and being provided with holes or openings to lead the gas into the furnace or drum.

The principal object of the invention is to provide a process and a device whereby an effective packing action is attained at the contact place between the gas supply box and the drum so as to reduce or eliminate losses of heat or gas at this place.

With this and other objects in view the process according to the invention consists in supplying to the furnace or drum in the manner set forth above, that is from the stationary gas supply boxes through openings or slots in the shell covered by the charge along whole or approximately the whole length of said shell, two or more gases of different temperatures introduced into and passed through the charge, the gas or gases of the lower temperature surrounding the 'gas of higher temperature andhaving a pressure in relation to 3 that of said gas of higher temperature as to prevent the latter from escaping laterally.

By this process such heat losses are eliminated which arise when gas of higher temperature escapes at the contact place between the gas supply boxes and the furnace or drum or takes its way unutilized below the charge past same or through its thinner portions. The inevitable gas leakage will, according to the invention, exclusively depend on the gas or gases of lower temperature, whereas the gas of higher temperature is forced. to pass through the thicker portions of the charge and, thus, will be utilizedfor the heat treatment to the highest possible degree.

Part of the gas or gases of lower temperature may be permitted to'pass through the fumaceor drum to be utilized to cool the charge.

In order to reduce the gas losses at the contactplace between the rotating furnace or drum andthe stationary gas supply boxes gas or gases oflower temperature may, according to the invention, be introduced into a packing slot sur-- rounding the communicating or outlet opening of said boxes to the furnace or drum in such a quantity as to prevent gas of higher temperature from entering said packing slot and escaping 5 through same.

In order to carry out' the process above de-' scribed the rotating furnace or drum is so arranged as to permit the introduction into same of two'or more gases of difierent temperatures 10 from gas supply chambers or boxes and along the whole or approximately the whole length of the shell in such a manner that gas of lower temperature surrounds wholly or in part gas of higher temperature. 15

The above-mentioned packing slot may be formed by providing the furnace or drum and the gas supply boxes with opposed parallel packing surfaces or the like, said surfaces being so spaced as to form between them a packing slot of the 20 desired width.

In such cases where the gas supply boxes are arranged below the furnace or drum and, consequently, there is a risk of any material which may fall through the openings or slots in the shell entering said boxes and causing disturbances in the course of the process, it is suitable to provide buckets or similar members on the outside of the shell, said buckets catching such material and delivering it to suitable collectingmeans or to the interior ofthe furnace or drum. Preferably, in such cases, said members orbuckets are so constructed as to form the required contact surfaces against the corresponding surfaces on the gas supply boxes.

The invention will be more fully described with reference to the accompanying drawing in which connection also other features characterizing same will be set forth.

In the drawing:-

Fig. l is a cross-sectional view of a furnace or drum arrangement according to the invention.

Fig. 2 is a cross-sectional view of the drum of another embodiment of an arrangement according to the invention.

Fig. 3 is a longitudinal sectional view of the furnace or drum arrangement shown in Figs.

1 and 2.

Referring to Fig. 1, reference numeral I designates the perforated shell of the drum provided on its outside with buckets or similar members 2;. The buckets '2 comprise each a base'portion 5, a radially. extending portion 3 and a cylindricallycurved portion 4 having at itsfree end an inwardly directed flange i. Openings or slots surface 9 co-operating with corresponding surfaces 4 ofthe buckets 2 of the drum I so as to form between said surfaces a packing slot H. Openings l in said end surface connect the chamber H with said packing slot H. The furnace or drum l is by means of roller rings l3 journalled on rollers 14, andarran'ged below the furnace or drum is a screw conveyor IS.

The device operates as follows: Gas of higher temperature is introduced into the chamber 8 and enters the drum I through the slots l and holes or openings in the shell covered by the charge. In the drum said gas passes through the charge and escapes then through other holes or openings in the shell not covered by the charge. Gas of lower temperature is introduced into the chamber l2 and passes through the openings it! into the packing slot ii creating in said slot a pressure suflicient to prevent .gas from chamber ii to escape through the slot. Part of the gas of lower temperature escapes through the. slot and will be lost, whereas the remainder passes into the drum l through the slots accordingly as said slots are passing along during the rotation, said gas moving upwards through the charge, thus preventing gas of higher temperature from escaping laterally. Any material which may fall through the holes or openings in the shell will be caught by the. buckets 2 and, during the rotation, be moved past the openings of the gas supply box, to be delivered, before the revolution is completed, to the conveyor l5 which collects the material and conveys it to any desired place.

In the modification shown in Fig. 2 the shell 5 of the drum is formed by plates B6 in part overlapping each 'other and forming between them openings ii for the passages of the gases into the charge. In this embodiment any material which has been caught by the buckets? is returned to the interior of the drum l through the slots ll, when, during the rotation, said slots attain their uppermost position. This construction of the shell of the drum may often be preferred in treating material not especially sensible to superheating, whereas the device shown in Fig. 1 ought to be preferred in treating sensible material, in which case it may be of advantage to remove from the process such particles that have fallen through the holes or openings in the shell.

As already mentioned, Fig. 3 is a longitudinal sectional view of the furnace or drum, the same reference numerals being used in this figure as in Figs. 1 and 2.

What we claim is:-

l. A device for treating a charge of material by hot gas, comprising a rotatable drum having a perforated shell, means to introduce a charge into said drum, means to remove the charge treated from said drum, a gas'supply box having an outlet opening communicating with perforations of said shell, means to supply a gas of relatively higher temperature to said box and therefrom to the drum, a packingslot between the gas supply box and the shell and surround- 5 ing said outlet opening of the box, and means to introduce a gas of relatively lower temperature into said packing slot in a quantity sufficient to prevent the gas of higher temperature? from escaping through said packing slot; 10 2. A device for treating a charge of material by hot gas, comprising a rotatabledrum having a perforated: shell and on its outside means for collecting material falling through said perforations and for returning such material into the drum, means to introduce a charge into said drums, means to remove the charge treated from said drum, a gas supply box comprising adjacent stationary chambers placed about the circumference of the rotating drum and opening into perforations offsaid shell, means to supply a gas to said-box and therefrom to the drum, and independent meansto so supply another gas to said box that it surrounds the first-mentioned gas at the entrance of the latter into the drum.

3. A device for treating a charge of material by hot gas, comprising a rotatable drum having, a perforated shell, means to introduce a charge into said drum, means to remove the charge treated from said drum, a gas supply box open- 30.

ing into perforations of said shell, means to supply a gas of relatively higher temperature to said box and therefrom to the drum, independent means to so supply another gas of relatively lower temperature to said box that it surrounds the gas of higher temperature at the entrance of the latter into the drum, and means outside the shell for collecting material falling through the perforations and for returning such material into the drum, said last-mentioned means comprising buckets having a radially extending portion and a cylindrically curved portion parallel .to the shell and in continuation to said radial portion said last-mentioned portion having at its free end an inwardly directed flange, 4,5v

openings being provided between said buckets to lead the gas to the shell.

- 4. A device for treating a charge of material by hot gas, comprising a rotatable drum having a perforated shell, means to introduce a charge into said drum, means to remove the charge treated from said drum, a stationary gas supply box comprising acentralchamber and a lateral chamber on each side of and adjacent to said central chamber, said chambers being placed 

